Armoured Cable

Discussion in 'Electricians' Talk' started by Derek JC, May 23, 2007.

  1. Derek JC

    Derek JC New Member

    Have been discussing with my electrician about his proposed cable run from my house to an outbuilding some 20 metres away from the main incoming fuses.

    The current cable run is in 10mm T+_E, suspended above the drive on a secondary supporting cable between the two buildings.

    He is going to replace the cable with a 16mm armoured cable but what I want to know is can he run this overhead between the buildings and what are the regs on this or does it HAVE to go underground??

    Cheers
  2. Sparky Mike

    Sparky Mike New Member

    Well it depends if the area under the cable run is accessable to vehicular traffic.

    If it is then the minimum height is 5.8m, if not you can bring it down to 3.5m.

    I assume you are going to support it with a dedicated catenary wire? Is this what you meant by 'secondary supporting cable'? Although 16mm2 armoured over 20m with no intermediate support is quite a weight!

    Might be better to bury it.
  3. ally1957

    ally1957 New Member

    p.v.c cable can be run overhead up to a max length of 30 metres. Height restrictions apply if vehicles pass underneath 5.8 meters.
    Using armoured cable will increase cost,a catenary wire is sufficient to comply with regs
  4. Coloumb

    Coloumb Active Member

    Pvc cable should not be exposed to direct sunlight.
  5. Sparky Mike

    Sparky Mike New Member

    Well it depends if the area under the cable run is
    accessable to vehicular traffic.

    If it is then the minimum height is 5.8m, if not you
    can bring it down to 3.5m.


    Are you on a farm by the way? Because if you are then it's 5.8m if vehicles are accessable or not.
  6. ally1957

    ally1957 New Member

    Pvc cable should not be exposed to direct sunlight.

    Table 3A OSG states otherwise
  7. Derek JC

    Derek JC New Member

    No it's not a farm.

    The cable will be run alongside the house to the point where it has to cross the driveway to the other building. The out-building that the cable will be feeding is only 3 metres high itself, so I can't see how I will get 3.5m, let alone 5.8m.

    What are the regs on burrying it then? The reason we are trying to avoid burrying it is because the gas main lies under the proposed route.
  8. Coloumb

    Coloumb Active Member

    Pvc cable should not be exposed to direct
    sunlight.

    Table 3A OSG states otherwise

    EG to the BR states otherwise again.

    Anyway, its a fact: UV rots PVC.
  9. ally1957

    ally1957 New Member

    Grey area. Anyway OP has moved the goalposts, sounds like he doesn't trust his spark.
  10. Derek JC

    Derek JC New Member

    I take it that XLPE insulation isn't affected by UV rays then?
  11. M107

    M107 New Member

    If the outbuilding is only 3mtrs high, then use a timber/metal post to make up the .5 of a meter.

    Or ask spark if he would be prepared to install swa on catinary at 3mtrs height & sign off as a deviation on cert.
  12. Sparky Mike

    Sparky Mike New Member

    What are the regs on burrying it then? The reason we
    are trying to avoid burrying it is because the gas
    main lies under the proposed route.

    There really isn't a one-off answer to that i'm afraid, 600mm down is the generally accepted minimum but it's quite site specific.
  13. Derek JC

    Derek JC New Member

    Cheers for the advice.... i think we're gonna find someone who will install on cantinary at 3.5m using a post on the roof of the outbuilding to raise it up. It's not a public road, or even a road as such and it's pretty difficult to drive a car across that part of the drive anyway as it's too narrow, so I think 3.5m will be more than ok.
  14. pcelectrics

    pcelectrics New Member

    Can't help wondering why you're upgrading the supply cable from 10 to 16?

    Armoured cable doesn't have to be buried. It can be run on the surface. Is there a route that could be taken around the perimeter of the property?

    If not and it is necessary to go the suspended route, then I would suggest using split concentric for the suspended section. It's black sheath is better for UV resistance than the grey of T&E and it doesn't have the weight of the steel armour (16mm copper conductors will be quite heavy any way). The section at ground level should still be SWA.

    With regards the height, I was told that these regs applied to areas of public access. On private land between (domestic) buildings it is not necessary to adhere too strictly. Obviously about 2.4m should be a minimum in any situation. I don't see why you couldn't go with 3m and put it down as a deviation on the EIC. It would be necessary to assess whether this was safe in your particular circumstance.
  15. Derek JC

    Derek JC New Member

    The voltage drop on the cable and length of run was worked out and a 16mm cable was recommended.

    The building being supplied by this cable contains 2 ring circuits, lighting and a combi boiler.
  16. sinewave

    sinewave Screwfix Select

    1st point is UV rays do damage PVC cables but it's relevant to white flex or grey T/E.

    If you use Black PVC cables then your OK! ;)

    2nd Your minimum burial depth if you choose to bury the SWA would be 500mm not 600mm.

    Depth is actually 460mm from the top of the buried cable to ground level, so allowing for cable thickness and trench unevenness then 500mm give the required tolerances.


    It's no big deal digging near a gas service, (they aint made of glass ya know!) so just bury it and av done with it! :)
  17. fooman

    fooman New Member

    The voltage drop on the cable and length of run was
    worked out and a 16mm cable was recommended.

    The building being supplied by this cable contains 2
    ring circuits, lighting and a combi boiler.

    how was that worked out ?

    Theres more loading on an electric shower than that lot and you only use 10mm for that. 20 meters is not that far 10mm would be fine.
  18. wally2

    wally2 New Member

    sounds like its a bit heavy to suspend so as other posts say its best to bury it. The other option of course would be to use 3 hard drawn copper cables on insulators eighter end, less weight & self supporting & probally smaller csa.
  19. fooman

    fooman New Member

    The other option of
    course would be to use 3 hard drawn copper cables on
    insulators eighter end, less weight & self supporting
    & probally smaller csa.

    bit ott for a shed an outbuilding :^O
  20. wally2

    wally2 New Member

    just another view foo (that rymes well)unlikely Id do it myself

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